Electroluminescent element



Julx 10, 1962 T. L. C. VAN GEEL ETAL.

ELECTROLUMINESCENT ELEMENT Filed Des. 9, 1959 FIG.

INVENTORS TIL.C. VAN GEEL H. J.M. JOORMN AGENT tates Ths invention relates to electroluminescent cells or elements, that is to say elements comprising a layer of electroluminescent materal which is provided between two conductive layers serving as electrodes.

Elements of the above type have been known for a couple of years already and have been used as light sources, for example for purposes of decoraton or indication. The electrolumnescent layer of such elements in most of the cases consists of a powdery electroluminescent matcrial, embedded in a medium having a high dielectric constant, for example a synthetic resin When between the electrodes, provided on either.side of this electroluminescent layer, an alternating voltage of sufficient value is set up, the electroluminescent material luminesces. Naturally the emission is dependent on the nature of the electroluminescent material. These materials are practically invariably zinc sulphide, cadmium sulphide or znc cadmium sulphide each activated with some activator or other. An unpleasant property of the electroluminescent material in general and of the above sulphides in particular, is that they are highly sensitive to moisture. The action of moisture on the electroluminescent layer results in a strong decrease of the output, after a comparatively short period of time. Ths phenornenon was already ascertained some time ago and various measures have been that the electroluminescent material is enclosed in a sealing agent, for which several materials were suggested,

In order to obtain a suflcient inter alia synthetic resins. amount of light from the elements, it is naturally undesirable to enclose the elements entirely. Therefore, the elements have been built up as follows. On a transparent carrier body, that is to say permeable to the radiation produced in the element, for example quartz, glass or synthetic resin, a conductive layer is provided which is like- Wise transparent. On this layer which is very thin, the electroluminescent layer is then provided which, on the other side, is covered with the second electrode. Ths electrode may'be opaque in which case one has an eleinent which can radiate to one side only, which, in general, is suiiicient. Ths latter metal layer can be applied in a simple manner, for example by providing a metal, for example aluminum, by spraying or evaporating. In order to ncrease the output in the direction of radiation, it has also been suggested already t0 apply a thin layer of titanium dioxide between the latter metal layer and the electroluminescent layer. Ths layer at the same time increases the break-down voltage of the element.

In an element built-up in this manner, the moisturerepellent sealing agent is applied both on the sides and on the rear-side.

At any rate care should be taken that, starting from any point of the electroluminescent layer, the minimum length of the -path through the envelope of the element outwards omnidrectionally is so large that the influence of the moisture of the atmosphere remains below that value at which decrease of the electrolurninescence may occur. At the periphery of the electroluminescent layer, the sealing layer must consequently extend in line with the electroluminescent layer so far that this length of path is available. As a result of this, the total size of the element in this direction is increased. With large elements this in- 3@43fi79 Patented July 10, 1962 crease of the size naturally plays -a smaller part than in the case of small elements. For, with these small ele ments, the increase, in percentage, is much more con siderable than with elements havng a large surface. Also in the direction in which the radiation is to be emitted, the length of path through the sealing layer should meet the minimum length, as a result of which the element becomes thicker. The carrier may then be chosen thicker, as a result of which a greater absorption of the emitted radiation Will naturally occur, or the sealing layer may be partially providecl on the front side of the carrier. In this case, however, even more of the useful radation sur fase will be lost.

An electroluminescent element according to the invention is built up in such a manner that the above drawbacks occur to considerably lesser degree.

An electroluminescent element according to the invention comprises an electroluminescent layer having on either side anelectrode, of which at least one is trans parent, and an envelope partially consisting of a moisturerepellent sealing agent and partially of a materialwhich, when of equal thickness, is less permeable to moisture than the sealing agent, and is characterized in that the part of the envelope not consisting of sealing agent has the shape of a container comprising the electroluminescent layer and the electrode, and that the sealing agent is applied in the container in a manner such that the minimum length of pathfrom any point of the electroluminescent layer outwards via the sealing agent is larger than the smallest thickness of the part of the envelope not consisting of sealing agent.

Preferably the minimum length of path from any point of the electroluminescent layer outwards is at least three times as large as the smallest thickness of the part of the envelope not consisting of sealing agent.

Here, as Well as in the already known form of an electroluminescent element, the sealing agent should meet various requiremnts. Naturally, low moisture perme. ability is very important. In addition, the sealing agent should adhere well to the part not consisting of sealing agent, it should be easy of deformation, be radiationresistant, that is to say retain its goed properties also during use when it is subjected to the radiation of the electroluminescent layer, and be inert with respect to the electroluminescent material and the electrodes. Qute a series of materials have been tested as to these properties and it has been found that ethoxylenic resins, particularly the cast resins, give good satisfaction. In addition, it is also possible to use polyesters, whether modified or not, combinations of natural and synthetic resins, or phenylic resins. All these materials are moisture tight, it is true, but only if they are applied in a comparatively thick layer, in general exceeding 5 min. Ths minimum thickness is an absolute measure, which is entirely independent of the size of the electroluminescent element. As already stated above, the sizes of the known elements are increased by this minimum thickness, in a plane parallel to the electroluminescent layer. S0, if, for example, one has an element of, say, 1 cm, diameter, which is to be used for a round push-button, this element is increased by 5 mm. omnidirectionally. The total diameter consequently becomes 2 cm. of which only one half emits radiation.

S0, for the container-like part of the electroluminescent element according to the invention, materials should be used which are less permeable t0 moisture than the sealing agents. Suitable materials are, for example, glass and quartz. In general, the thickness of these materials may be considerably smaller than the minimum thickness of the sealing agent because they are considerably better moisture-tight. At any rate, an improvement is already obtained, when they are better than the sealing agents and andthe electrode may be paque.

efiect, it will now be described in greater detail with reference to the accompanying drawing, in which:

FIGURE 1 shows one embodiment of a known element to illustrate the principle underlying the invention.

FIGURES 2 to 6 show embodiments of an electroluminescent element according to the invention.

In FIGURE 1, the carrier, for example of glass, of the electroluminescent element is indicated by 1. This carrier has a transparent 'electrode 2, for example conductive stannic oxide. The electroluminescent layer with the binding agent is indicated by 3 and the second elec trode, whether or not transparent, by 4. In order to exclude the electroluminescent layer from the atmosphere, it has been suggested to envelop the element with a layer of sealing agent 6. This layer should have snch a form and thickness -that, starting from a point 5 at the periphery, the minimally permissible, that is to say, sufliciently closing thickness, in this case equalling a, has to be traversed to all sides where the atmosphere can be reached via thesealing agent 6. In the figmre the various directions a are plotted. Starting from'point 5 downwards and round the corner of the glass plate 1, naturally also the distance to the atmosphere shonld be at least equa1 to a. The result of this minimum requirement is that 'the total width b equals the width c of the actual radiating element plus 2a. extends also at the front of the element, apart of the surface having the diameter c becomes less permeable to If, in addition,the s ealing layer the emittedradiation. This can natural-ly he met by giving the carrier 1 the thickness a. In that case, however, a great absorption of: the emitted radiation in the carrier 1 is the result.

The thickness a is also requirecl at the back of the ele ment, since the 'electrode 4 does not close the layer 3 in asufliciently moisture-tight manner. However, in this direction a large thickness is mostly little disturbing.

Anther possibility to meet the reqnirernent of separating the;edge of the electrolurninescent layer 4 from the atmosphere by a thickness of the sealing agent at least equalling a in line with the plane of the electroluminescent layer 3 conssts therein that the electrblnrninescent layer 3does not extend any further than the line '77,

Which is at a distancea from the edge of the element. Also in this case, however, the active surface of the element is considerably smaller than the total surface of the element.

FIGURE 2 shows an embodiment of an element according to the invention in which 8 ndicates a containerconductive stannic oxide, the electrolurninescent layer 11 and the electrode 12, are carried by the container 8. The radiation of this element may be to one side or two sides. Dependent on this, at least the bottom of the container 8 or the s ealing agent 9 must consequentlybe permeable to the radiation. If the radiation is to be emitted to the back-side, the electrode 12 must, naturally, be transparent Preferably, however, the radiation will be emitted throngh the bottom of the container 8, since it may be considerably thinner.

URE 2 the round glass container 8 has an Outer diameter of mms., an inner diameter of 28 mms. and a thickness of 1 mm. The condnctive layer 10 consists of stannic oxide and the conductive layer 12 of silver-powderpaint. The electrolnrninescent layer 11 consists of ZnS activated with Cu with urea resin as binding agent. The sea-ling agent 9 consisting of aethoxylene resin has a tliCkness of 5 mms.

It is clcar from FIGUREZ that the total width of the element with the envelope for the same useful surface as shown in FIGURE 1 is considerably smaller than the dimension b in FIGURE 1. The dimensions in FIG- URE 2 have not all of them been enlarged equally strengly, since the layers 111, 11 and 12 are very thin and have, for clearness sake, been enlarged far more strongly than the thickness of the parts 8 and 9. At any rate it goes forward trom FIGURE 2 that the minimum length of path from any point ofthe electroluminescent layer outwards via the sealing agent 9is larger than the smallest thickness of the container-shaped body 8, namely approxi mately 4 times as large.

In the embodiment shown in FIGURE 3, an additional carrier 17, for example of the same material as the container 15, is provided between the container-shaped body 15 and the first electrode 16. The electrode 16, the electroluminescent layer 18, and the second electrode 19 are applied to the carrier before the whole of the parts 16 to 19 is positioned in the container 15. It is as a matter of tact sirnpler to provide the electrodes and the electroluminescent material on a flat surface than on the bottom of the container 15'. After the whole of the parts 16 to 19 has been made, it is placed in the container 15 and the sealing agent 29 is provided. Flexible-strip-like current supply eondnctors are indicated by 21 and 22.

The ern'oodiment according to FIGURE 4 shows great resemblance to the ern-bodiment shown in FIGURE 3. The additional carrier 23, however is not provided on the side of the bottom of the container 24, but on the side rernote therefrorn. The sealing agent is indicated by 25, the electrodes by 26 and 27 respectively, the electroluminescent layer by 23, and the current supply conductors by 29 and 38 respectively.

FIGURE 5 shows a form in which the electroluminescent layer 31 and the electrodes 32 and '33, provided on either side of the layer 31, are provided between the inside of the bottom of the container-shaped body 34 and the outside of the bottom of a second container-shaped body 35, preferably consisting of the same material as the container 34. The aperture 36 between the two parts 34 and 35 is filled with the sealing agent. The heght of this aperture 36 exceeds the mirdmtnnthickness of the container 34. In this embodiment an even better moistnretightclosnre is achieved than in the embodirnent shown in FIGURES 2, 3 and 4. If desired, a disc of a thickness equal to the height of the aperture 36 may be used instead of the contaner-shaped part 35. However, if the element is to emit radiation to either side, the embodiment shown in FIGURE 5 is of advantage. FIGURE 6 shows an ernbodiment of an electroluminescent element according to the invention which shows great resemblance to that of However, in the manufactnre the whole FIGURE 5. of electrodes and electrolnrninescent layer is not built up,

as shown in FIGURE 5, on the inside of the bottom of the 0uter container, but on the outer side of the bottom of the inner container. In this figure, the outer container is indicated by 37, the inner container by 38, the electrodes by 39 and 46 respectively, and the electrolurninescent layer by 41. Between the electrode 40 and the electroluminescent layer 41 is a layer 42, which well refiects the radiation consequently be transparent.

emitted by the electroluminescent layer. For visible radiation, this layer consists, for example, of titanium-dioxide. In this embodiment the radiation is ernitted through the bottom of the container 37 and the electrode 39 must the two parts37 and 38 is closed by the sealing agent.

As sealing agents the already known materials may be used. If necessary, a softening agent may be added to The aperture 43 between these materials to avoid tension being exerted on the container-shaped elements. In tact some of the known sealing agents expand on cooling or polymerisation.

In special cases, only the bottom of the container-shaped parts could be made transparent to the radiation. The upright edges could then consist, for example, of metal which is melted to the bottorns or connected in some ether way in an entirely moisture-tight manner.

What is claimed is:

1. An electroluminescent element comprising a cupshaped supporting glass container having bottom wall and upwardly extending wall portions, a layer of moisturesensitive electroluminescent material mounted within sad container and extending generally parallel tothe sad bottom wall portion, electrodes contacting opposite sides of the electroluminescent layer, one of sad electrodes being transparent flexible conductive leads connected to electrodes, and a moisture-impervious body of a sealing agent secured to the container wall portions and sealing the electroluminescent layer within the container and surrounding the conductive leads, sad sealing agent having a thickness sufliciently large to prevent external moisture trom reachng the electroluminescent layer and at which the minimum length of path front any point of the electroluminescent layer via the sealing agent to the outside is larger than the smallest thickness of a container wall portion, sad container being moisture-impervious and being. constituted of a material whose comparative moisture imperviousness for a given thickness is substantially greater than a comparable thickness of the sealing agent.

2. An electroluminescent element comprising a cupshaped container having a transparent bottom wall and upwardly extending wall portions, a layer of moisturesensitive sulphide-type electroluminescent materal mounted within sad container and extending generally parallel to the sad bottom wall po1tion, electrodes contacting opposite sides of the electroluminescent layer, the electrode adjacent the bottom wall being transparent, and a mois ture-impervious body of a sealing agent secured to the container wall portions and sealing the electroluminescent layer within the container, sad sealing agent having a thickness sufiiciently large to prevent external moisture TOIII reaching the electroluminescent layer and at which the minimum length of path from any point of the electroluminescent layer via the sealing agent to the outside is at least three times larger than the smallest thickness of a container wall portion, sad container being moistureimpervious and being constituted of a material whose comparative rnoistureimperviousness for a given thickness is substantially greater than a comparable thickness of the sealing agent.

3. An element as set forth in claim 2 wherein the cupshaped container is constituted of a material selected from the group consisting of glass and quartz, and the sealing agent is a synthetic resin.

4. An electroluminescent element comprising a cupshaped glass container having a bottom wall and upwardly extending wall portions, a transparent electrode on the inside bottom wall, a layer of moisture-senstive electroluminescent sulphide material mounted within sad container over the transparent electrode, another electrode contacting the opposite side of the electroluminescent layer, and a moisture-im-pervious body of an in situ cast synthetic resin secured to the container wall portions and completely filling the remainder of the container and sealing the electroluminescent layer within the container, sad resin having a thickness sufliciently large to prevent external moisture -frorn reaching the electroluminescent layer and at which the minimum length of path trom any point of the electroluminescent layer via the resin to the outside is much larger than the smallest thickness of a container wall portion, sad container being moisture im pervious and the glass of which it is constituted having a comparative moisture-imperviousness for a given thickness substantially greater than a comparable thickness of the resin.

5. An electroluminescent element comprising a cupshaped glass container having bottom wall and upwardly extending wall portions, a glass support, an electrode on sad support, a layer of moisture-sensitive electroluminescent material on sad support over sad electrode, sad support being mounted within sad container and extending generally parallel to the sad bottom wall portion, another electrode contacting the opposite side of the electroluminescent layer, one of sad electrodes being transparent, and a moisture-imperv-ious body of an in situ cast synthetic resin secured to the container wall portions and completely filling the remainder of the container and sealing the electroluminescent layer within the container, sad resin having a thickness sut'ticiently large to prevent external moisture from reaching the electroluminescent layer and at which the minimum length of path from any point of the electroluminescent layer via the resin to the outside is -rnuch larger than the smallest thickness of a container wall portion, sad container being moisture-impervious and the glass of which it is constituted having a comparative moisture-imperviousness or a given thickness substantially greater than a comparable thickness of the resin.

6. An electroluminescent element comprising a first cup-shaped container having bottom wall and upwardly extending wall portions, a second, smaller cup-shaped container nested within the first container but spaced from the latter, a. layer of rnoisture-sensitive electroluminescent material mounted between sad nested containers and extending generally parallel to the sad bottom wall portion, electrodes contacting opposite sides of the electroluminescent layer, one of sad electrodes being transparent, and a moisture-mpervious body of a resin secured to and between both containers and sealing the electroluminescent layer between the nested containers, sad resin having a thickness sufiiciently large to prevent external moisture afrom reaching the electroluminescent layer and at which the minimum length of path from any point of the electroluminescent layer via the resin to the outside is mueh larger than the smallest thickness of a container wall portion, each of sad containers being moisture-impervious and being constituted of a material whose comparative-imperviousness for a given thickness is substantially greater than a comparable thickness of the resin.

References Cited in the file of this patent UNITED STATES PATENTS 2,183256 Gabler Dec. 12, 1939 2,222,788 Touceda et al. Nov. 26, 1940 2,774004 laffe Dec. 11, 1956 2,863,061 Destriau Dec. 2, 1958 FOREIGN PATENTS 740,473 Great Britain Nov. 16, 1955 798,504 Great Britain July 23, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3.043.979 July 10, 1962 Theodorus Leonardus Cornelis van Geel et al, It is hereby certified that error ap paars in the above numbered patent. requiring correction and that the said Letters Patent should raad as corrected below.

Column 3, line 31,

before "the" column 5, line 17,

insert as shown, after "to" insert the Signed and sealed this 26th day of March 1963.

(SEAL) Attest:

ESTON G. JOHNSON DAVID L. LADD Attesting Officer Commissioner of Patents 

